Codewars. Python

binomial-expansion-3kyu.py

from math import factorial

def expand(expr):
    print(expr)
    expr = expr.split("^")   # Splitting expression
    expr[0] = expr[0][1:-1:1]
    m = list(expr[0])
    m.reverse()
    sign = ""

    for i in range(len(m)):
        if m[i] == "-" or m[i] == "+":
            if m[i] == "+": sign += "+" 
            else: sign += "-"
            m.insert(i," ")
            m.insert(i+2," ")
            expr[0] = "".join(reversed(m))
            break
    if expr[0].split()[0][0:-1:1] == "": a = 1 # conversion to coefficients and unknowns
    elif expr[0].split()[0][0:-1:1] == "-" and len(expr[0].split()[0][0:-1:1]) == 1: a = -1
    else: a = int(expr[0].split()[0][0:-1:1])
    koef = expr[0].split()[0][-1]
    if sign == "-": b = -int(expr[0].split()[2])
    else: b = int(expr[0].split()[2])

    if expr[1] == "0": return ("1")

    elif expr[1] == "1": return ("".join(expr[0].split()))

    elif int(b) == 0: expr[0] = "".join(expr[0].split()); return (f"{koef}^{expr[1]}") if a == 1 else (f"{str(a)+koef}^{expr[1]}")

    pusher = []

    n = int(expr[1])
    i = 0
    for k in range(n+1):  #newton's binomial theorem

        val = ""
        val += (str((factorial(n) // (factorial(k) * factorial(n-k)))*(b**k)*(a**(n-k))) + koef +f"^{n-k}")
        if val[0] == "-": pusher.append(val)
        else: pusher.append("+"+val)

    res = ""

    for i in range(len(pusher)): #conversion in string
        if i == 0:
            if pusher[i][1] == "1" and pusher[i][2] == koef and pusher[i][0] == "-":
                res += (pusher[i][0]+pusher[i][2::])
            elif pusher[i][1] == "1" and pusher[i][2] == koef and pusher[i][0] == "+": 
                res += (pusher[i][2::])
            elif pusher[i][0] == "+":
                res += pusher[i][1::]
            else:
                res += pusher[i]
        elif pusher[i].split("^")[1] == "1":
            res += pusher[i].split("^")[0]
        elif pusher[i].split("^")[1] == "0":
            res += (pusher[i].split("^")[0][:-1:])
        else:
            res += pusher[i]
    return res #sorry for shitty code in this kata, i hope in future ill write better